160 ALASKAN GLACIER STUDIES FOURTH GLACIEB General Description. Until 1909 we had not visited this glacier, though we knew of its •existence, partly from the Canadian Boundary Commission map,1 and partly from visiting the large, milky glacial stream which issues from it and enters the head of Russell Fiord. It was photographed and roughly mapped by the Canadian topographers in 1895 and was well known to the prospectors who crossed it in 1898, and in smaller numbers almost every year since; but they have left us no description of the conditions which they encountered in their journeys over its surface, except the inference that, being passable, it was not greatly crevassed. They went over this glacier highway in sufficient numbers in 1898 to warrant the establishment of a store on the shores of Russell Fiord near the point where the glacial stream emerges, relics of which are still to be seen. Blackwelder saw the glacier in 1906 from a mountain spur some miles south, noting the moraines upon its surface and suggesting a new name (Beasley Glacier) instead of the one generally used. This name3 has recently been discarded by the U. S. Geographic Board for reasons stated in Chapter II. The glacier was mapped more accurately and photographed from peaks on three sides by the Boundary Survey party in charge of Fremont Morse in 1906, And the sketch map of the glacier (Fig. 15) is reproduced from their unpublished map. The Fourth Glacier is fed by at least four short tributaries, each about 2£ to 3 miles long, that unite to form the trunk glacier (PL LXXXVI, B), which has a length of 8J miles, a width of over a mile, and terminates approximately 500 feet above sea level, three or four miles east of Russell Fiord. The two Boundary Survey maps show it as a through glacier connected with the upper portions of the Hidden and Yakutat glaciers, which in turn connect with glaciers descending to the Alsek valley. The through glacier divides between it and Hidden Glacier rise 3880 and 3750 feet respectively, that to Yakutat •Glacier about 3500 feet. Over this latter pass prospectors state that one could start at the terminus of the Fourth Glacier and find open, ice-filled valleys over which sledging is not difficult, across various divides, and down different glaciers into the Alsek Valley. Fourth Glacier thus has complex relations with other glaciers, because these coast mountains receive such heavy snowfall that the valleys are drowned in ice, forming a network of through glaciers. Observations in 1909. That part of the Fourth Glacier which lies within the range of our observation is the lower two or three miles, or below where the tributaries from the direction of Hidden Glacier unite with those from the east. In the upper portion of this •observed section the glacier emerges from a broad valley enclosed in mountains of no great height, which because of the fact that they face the ocean, and lie not far from it, do not "bear a heavy burden of snow. Farther back the mountains rise higher and the snow •cover is more extensive. The outer portion of the glacier is made by the union of two pairs of arms, and photographs show three medial moraines that are formed by lateral moraines from these tributaries. Above the terminus of the glacier two medial moraines swing over to the eastern margin and become lateral, the one on the east side being light-colored and that on the left dark-colored. A narrower medial moraine rnaintaiTia a position near the east side.8 i Atlas of Award, Alaskan Boundary Tribunal, Sheet 21. «Blackwelder, E., Joutn. Geol., Vol. XV, 1907, pp. 417-418. * A medial moraine shown in the Boundary Survey photograph swings over to the west side; but we have no knowledge of its origin or relationships.